1. Field of the Invention
The present invention relates to a digital broadcast receiver for receiving digital broadcast signals such as terrestrial digital broadcast signals, BS (Broadcast Satellite) digital broadcast signals and CS (Communication Satellite) digital broadcast signals, and more particularly to a digital broadcast receiver having an OSD (On Screen Display) function.
2. Description of the Related Art
It is known that a conventional digital broadcast receiver for e.g. terrestrial digital broadcast can receive not only SD (Standard Definition) broadcast signals which are low resolution signals like analog broadcast signals, but also HD (High Definition) broadcast signals which are high resolution signals, and that the conventional digital broadcast receiver can output image data of high resolution to an HDTV (High Definition Television). The HDTV has an image format of 1080i (1920 horizontal pixels by 1080 vertical pixels, “i” standing for interlaced), and thus has the number of pixels more than four times as large as that of an SDTV (Standard Definition Television) for analog broadcast which has an image format of 480i (640 or 720 horizontal pixels by 480 vertical pixels), so that the HDTV can display images with a resolution of more than four times as high as that of the SDTV.
When receiving broadcast signals, the conventional digital broadcast receiver sends menu image data of common format to a television receiver, regardless of the resolution of the received broadcast signals and the resolution of the television receiver. More specifically, the conventional digital broadcast receiver generally outputs menu image data for various settings to the television receiver in full screen display format, regardless of the resolution of images on the television receiver and regardless of the screen size of the television receiver.
However, the conventional digital broadcast receiver has the following problems. According to the digital broadcast receiver as described above in which menu image data are unconditionally sent to the television receiver in full screen display format, it is unavoidable that the menu image data are sent to the television receiver in full screen display format even if the image resolution on the television receiver is high, and the screen size of the television receiver is large. Note here that if the received broadcast signals are those of HD broadcast, and if the television receiver is HDTV, characters in a menu image are unlikely to be corrupted or unidentifiable even when displayed by OSD (On Screen Display) in a sub-screen which is a smaller screen superimposed on a full screen. Accordingly, it practically does not cause any problems to display a menu image in a sub-screen by OSD if the screen size of the television receiver is large (for example 37 inch or larger). Thus, the conventional digital broadcast receiver has a problem that a user cannot input setting of menu items while watching broadcast images even in the case where it does not cause any problems to display a menu image in a sub-screen by OSD, because menu image data are unconditionally output to the television receiver in full screen display format.
Japanese Laid-open Patent Publication Hei 5-75944 discloses a digital broadcast receiver in which menu image data for various settings are sent to a television receiver in sub-screen display format, regardless of the resolution of images on the television receiver and regardless of the screen size of the television receiver. However, according to the digital broadcast receiver disclosed in this patent publication, it is unavoidable that the menu image data are sent to the television receiver in sub-screen display format even if the image resolution on the television is low. Accordingly, it has a problem that characters in a menu image displayed in the sub-screen are likely to be corrupted, and it is difficult for a user to identify characters in the menu image. In addition, the digital broadcast receiver disclosed in the above patent publication has a problem that it is further difficult for a user to identify characters in the menu image, because it is unavoidable that the menu image data are sent to the television receiver in sub-screen display format even if the screen size of the television receiver is small, and hence the size of the characters in the menu image displayed in the sub-screen becomes smaller.